At present, in the process for producing electronic devices, a masking vapor deposition method or an etching method by photolithography is mainly employed for the formation of a pattern of an electrode or a functional thin film. With respect to such conventional methods, problems have been pointed out such that enlarging the substrate is difficult, and the process is cumbersome.
In recent years, it has been proposed to apply a technique for selective coating utilizing the difference in wettability with a liquid to the patterning of a functional thin film. This is a method wherein a patterning layer comprising a region wettable with a liquid and a region hardly wettable with a liquid, is formed on a substrate surface, and then, on this patterning layer, a solution of a functional thin film-forming material is applied and dried, so that the functional thin film is formed only at the region wettable with a liquid. The method is intended to thereby prepare an electronic device such as an organic EL (electroluminescence) device or an organic FET (field-effect transistor) device.
As such a patterning layer for a functional thin film, a photocatalyst-containing layer comprising titanium dioxide and an organopolysiloxane, irradiated with ultraviolet light through a mask (e.g. Patent Document 1), or a layer comprising a fluoropolymer and a compound having a photoabsorption site such as a dye, irradiated with laser or irradiated with ultraviolet light through a mask (e.g. Patent Document 2) has, for example, been known. Further, a method for vapor deposition of a fluorinated coating agent through a mask has also been proposed (e.g. Patent Document 3).
Whereas, such a patterning layer will remain in the device even after completion of its role for patterning the functional thin film. Accordingly, such a patterning layer is required to have durability against the subsequent process steps and reliability not to adversely affect the properties of the electronic device even if it is present therein. Such properties required for the patterning layer may vary depending upon the particular device to be prepared or the particular place where the patterning layer is to be used. Among them, as a patterning layer for an electrode, the electrical insulating property becomes important.
In the techniques heretofore proposed, importance has been placed only on the properties as the patterning layer. Therefore, in patterning a source electrode and a drain electrode for an organic FET device, it is necessary to prepare a gate insulating film beneath the patterning layer.
On the other hand, a polyimide is excellent in heat resistance, mechanical strength, electrical insulating properties, chemical resistance, etc., and thus is used for various electronic devices. However, no case has been reported wherein a polyimide itself is used for a patterning layer as described above.
Patent Document 1: JP-A-2000-223270
Patent Document 2: JP-A-2004-146478
Patent Document 3: JP-A-2004-273851